Refining elements

ABSTRACT

Apparatus is disclosed for refining lignocellulosic material including a pair of refining elements facing each other for relative rotation to refine the lignocellulosic material passing through the refining gap between the refining elements. The refining elements include rows of projecting working pins with substantially circular cross-sections and strips projecting above the refining element surface and extending substantially circumferentially along the refining surfaces. The rows of projecting working pins are disposed at selected radial positions on the two refining surfaces so that they avoid contact with each other during relative rotation of the two refining surfaces.

FIELD OF THE INVENTION

The present invention relates to refining elements for use in disk-typerefiners for working, i.e. for defibering, refining or dispersinglignocellulosic fiber material in the form of chips or pulp. The workingof the lignocellulosic material can have the purpose to manufacture, forexample, recycled fiber pulp or mechanical pulp, such asthermomechanical pulp (TMP) and chemi-thermomechanical pulp (CTMP). Moreparticularly, the present invention relates to a pair of cooperatingrefining elements, which are intended to be positioned directly in frontof each other on opposed refining disks in a refiner of this kind.

BACKGROUND OF THE INVENTION

The working of fibrous material takes place in the refining gap formedbetween the refining elements on two opposed refining disks rotatingrelative to each other. The fibrous material is thereby subjected tomechanical action by working means on the refining elements, while itsimultaneously moves by the effects of centrifugal force. The workingmeans can be formed as continuous or discontinuous bars, teeth or insome other manner.

During the defibering of fibrous material in the form of chips, it isdesired for the chips to be disintegrated to individual fibers with aminimum of fiber shortening. Experiments have proved that theconfiguration of the refining elements in the inner portion of therefining gap is of great importance for the feed of the material throughthe refining gap as well as for the defibering process. During thedispersion of recycled fiber pulp, working is desired which does notcause any fiber shortening or reduction in the freeness value (CSF) ofthe pulp.

Working, which causes fibrillation and fiber shortening, occurs mostoften when the refining means are formed with bars, by the effect of theedges of the bars. Conventional refining elements with working means inthe form of bars with intermediate grooves can also result in anon-uniform flow of the material through the refining gap. This resultsin the load on the motor or motors driving one or both of the refiningdisks being uneven.

As a result thereof, the process will be difficult to control, and theenergy consumption increases. It can also effect the quality of theworked pulp.

SUMMARY OF THE INVENTION

These and other difficulties in the prior art have now been alleviatedby the invention of apparatus for refining lignocellulosic materialcomprising a first refining element including a first refining surface,and a second refining element including a second refining surface facingthe first refining surface thereby providing a refining gaptherebetween, the first and second refining surfaces being relativelyrotatable with respect to each other whereby the lignocellulosicmaterial can be refined while passing through the refining gap, thefirst refining surface including a first plurality of rows of projectingworking pins having a substantially circular cross-section and at leastone first strip projecting above and extending substantiallycircumferentially along the first refining surface, and the secondrefining surface including a second plurality of rows of projectingworking pins having a substantially circular cross-section and at leastone second strip projecting above and extending substantiallycircumferentially along the second refining surface, the first andsecond pluralities of rows of projecting working pins disposed atselected radial positions on the first and second refining surfaceswhereby the first and second pluralities of rows of projecting workingpins avoid contact with each other upon the relative rotation of thefirst and second refining surfaces. In a preferred embodiment, the firstand second pluralities of rows of projecting working pins are disposedat alternating radial positions with respect to each other.

In accordance with one embodiment of the apparatus of the presentinvention, the at least one first strip comprises a plurality of firststrips and the at least one second strip comprises a plurality of secondstrips.

In accordance with another embodiment of the apparatus of the presentinvention, the first and second pluralities of rows of projectingworking pins are substantially cylindrical, and include a rounded uppersurface distal from the first and second refining surfaces.

In accordance with another embodiment of the apparatus of the presentinvention, the at least one first and second strips are disposed alongan arc. Preferably, the at least one first and second strips aredisposed adjacent to the first and second pluralities of rows ofprojecting working pins on the first and second refining surfaces.

In accordance with another embodiment of the apparatus of the presentinvention, the at least one first and second strips extend continuouslyacross the entire first and second refining surfaces.

In accordance with another embodiment of the apparatus of the presentinvention, the at least one first and second strips extenddiscontinuously across the first and second refining surfaces.

In accordance with another embodiment of the apparatus of the presentinvention, the first and second refining surfaces each includes an innerradial portion and an outer radial portion, the first and secondplurality of rows of projecting working pins on the at least one firstand second strips being disposed on the inner radial portions of thefirst and second refining surfaces. Preferably, the apparatus includesworking means for the lignocellulosic material disposed on the outerradial portions of the first and second refining surfaces. In apreferred embodiment, the working means comprises a plurality ofradially projecting bars.

The present invention offers a solution to the above problems. Opposedcooperating refining elements are provided with projecting working meansin the form of pins with a circular cross-section. The pins on one ofthe refining elements are arranged to extend into the interspace betweenthe pins on the opposed cooperating refining element. The refiningelements are also provided with flow restrictions in the form of stripsextending substantially in the circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail in the followingdetailed description, which, in turn, refers to the accompanying Figuresillustrating an embodiment of refining elements according to the presentinvention, in which:

FIG. 1 is a top, elevational view of one of the cooperating refiningelements in accordance with the present invention;

FIG. 2 is a top, elevational view of a second cooperating refiningelement in accordance with the present invention;

FIG. 3 is a side, elevational view of a pair of refining elementscooperating in accordance with the present invention; and

FIG. 4 is top, elevational view of an alternative configuration of onerefining element in accordance with the present invention.

DETAILED DESCRIPTION

Referring to the Figures, in which like reference numerals refer to likeelements thereof, FIGS. 1 and 2 show cooperating refining elements, 10and 11, which are intended to be positioned on each of two opposedrefining disks in a refiner where the refining disks are rotary relativeto each other. The refining elements shown are provided with projectingworking means in the form of pins, 12 and 13, with substantiallycircular cross-section, which are arranged in several rows in thecircumferential direction. The rows of pins are located radially spacedfrom each other across the entire surface of the refining elements.These pins, 12 and 13, can alternatively be arranged only in an innerzone on the refining elements, 10 and 11. An outside located zone canthen be provided with conventional working means, for example bars 14.

The pins, 12 and 13, are arranged in at least two radially spaced rowsand be cylindrical with a diameter of from about 10 to 30 mm, preferablyfrom about 15 to 25 mm, with rounded tops. Their length is from about 10to 30 mm, preferably from about 15 to 25 mm. Alternatively, conical pinscan be used. In working position the pins extend transversely across therefining gap essentially all the way to the surface of the opposedrefining element.

The refining elements, 10 and 11, are also provided with flowrestrictions in the form of strips, 15 and 16, which substantiallyextend in the circumferential direction. Compared with the pins, thestrips are quite low, suitably from about 4 to 12 mm, preferably fromabout 6 to 10 mm. The strips can be placed relative to the pins alongarcs. Alternatively, they can be given a direction slightly deviatingfrom an arc, i.e. in which the radius increases or decreases along astrip. The strips can be continuous or discontinuous. Discontinuousstrips can extend between two pins, for example.

During the working of the material during its passage outward throughthe refining gap between the co-operating refining elements, 10 and 11,the material will be acted upon by the pins, 12 and 13, and strips, 15and 16, in a manner which yields a very uniform feed. At the same time,an effective but mild start of the defibration and, respectively,dispersion is obtained. The strips, 15 and 16, have an object ofeffecting the residence time of the material in the refining gap. Forthis purpose, the height and direction of the strips are of decisiveimportance. This favorable effect on the material implies that even anon-uniform supply of material is balanced in the refining gap, whichhas a stabilizing effect on the entire working process.

By positioning the refining elements according to the present inventionon the inner portion of the refining disks, conventional refiningelements can be arranged on the outer portion of the refining disks andthereby improve the stability of the material flow and motor load. Thisapplies also when the refining elements according to the presentinvention have an inner zone with pins, 12 and 13, and an outer zonewith conventional working means, for example in the form of bars 14.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

What is claimed is:
 1. Apparatus for refining lignocellulosic materialcomprising a first refining element including a first refining surface,and a second refining element including a second refining surface facingsaid first refining surface thereby providing a refining gaptherebetween, said first and second refining surfaces beingsubstantially planar and relatively rotatable with respect to each otherwhereby said lignocellulosic material can be refined while passingthrough said refining gap, said first refining surface including a firstplurality of rows of projecting working pins being substantiallycylindrical, having a substantially circular cross-section, having adiameter of from 20 to 30 mm and including a rounded upper surface, andat least one first strip projecting above and extending substantiallycircumferentially along said first refining surface, and said secondrefining surface including a second plurality of rows of projectingworking pins having a substantially circular cross-section and at leastone second strip projecting above and extending substantiallycircumferentially along said second refining surface, said first andsecond pluralities of rows of projecting working pins disposed atselected radial positions on said first and second refining surfaces andsaid at least one first and second strips extending discontinuouslyacross said first and second refining surfaces whereby said first andsecond pluralities of rows of projecting working pins avoid contact witheach other upon said relative rotation of said first and second refiningsurfaces.
 2. The apparatus of claim 1 wherein said first and secondpluralities of rows of projecting working pins are disposed atalternating radial positions with respect to each other.
 3. Theapparatus of claim 1 wherein said at least one first strip comprises aplurality of first strips and said at least one second strip comprises aplurality of second strips.
 4. The apparatus of claim 1 wherein said atleast one first and second strips are disposed along an arc.
 5. Theapparatus of claim 4 wherein said at least one first and second stripsare disposed adjacent to said first and second pluralities of rows ofprojecting working pins on said first and second refining surfaces. 6.The apparatus of claim 1 wherein said first and second refining surfaceseach includes an inner radial portion and an outer radial portion, saidfirst and second plurality of rows of projecting working pins and saidat least one first and second strips being disposed on said inner radialportions of said first and second refining surfaces.
 7. The apparatus ofclaim 6 including working means for said lignocellulosic materialdisposed on said outer radial portions of said first and second refiningsurfaces.
 8. The apparatus of claim 7 wherein said working meanscomprises a plurality of radially projecting bars.